Method of producing lens coating material



Mamh 27 1 945. J. H. REYNQLDS 293772fi39 METHOD OF PRODUCING LENS COATING MATERIAL Filed April 18, 1942 I A 5 I ISnnentor Patented Mar. 27, 1945 METHOD OF PRODUCING LENS COATING MATERIAL James H. Reynolds, Indianapolis, Ind., assignmto Radio of Delaware (lorporation of America, a corporation Application April 18, 1942, SerialNo. 439,455

5 Claims.

This invention relates to an improved method of producing a material for providing reflection reducing coatings on lenses or other optical surfaces.

In an application of Glenn L. Dimmick, Serial No. 432,836, filed February 28, 1942, entitled Reduction in reflection from glass (RCV Docket 8689), there is disclosed an improved reflection reducing coating for lenses and analogous parts. The said coating is evaporated from a mixture oi aluminum fluoride and calcium fluoride, which are in molecular proportions in the mixture. The Dimmick application also discloses the addition of aluminum oxide to the material for the purpose of securing proper characteristics of surface tension.

In the present invention I prepare a pure eutectic compound of the two fluorides by evaporation of a mixture of the constituents in a vacuum.

One object of the present invention is to provide an improved lens coating material.

Another object of the invention is to provide an improved method of making a lens coating materia Another object or the invention is to provide an improved method of making a pure lens coating material,

Other and incidental objects of the invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawing, in which the single figure is a view, partly in section, ofthe apparatus used in the performance of the method.

Referring to the drawing, the evaporating apparatus is provided with the usual base I andbell jar H which is in turn provided with an appropriate airtight sealing means I 2 for preventing leakage between the bell jar and the base. The base is provided with the usual exhaust pipe I 3, through which the apparatus may be evacuated, and with terminal connections l4 and I5 for the supply of electric current. The connections H and I5 are so constructed that appropriate attachment can be made thereto within the bell Jar.

On the connections l4 and there is supported a boat l6, which may be folded from appropriate thin metal, the ends being folded down as shown to make connection with the terminals i4 and IS. The boat It is preferably made of platinum, although an appropriate iron-chromium alloy may be used if desired. It will be apparent that if suflicient current is supplied through the connections it and IS, the boat It may be heated to w practically any temperature desired.

On the boat ll there are placed small insulating pieces I8 and I9, which may be, for example,

provided on the boat It, as they are not necessary for the purpose of the boat ll. However, these two boats may be made identical if desired. so that they may be interchanged according to the use to which they are to be put.

The mixture of calcium fluoride and aluminum fluoride in molecular proportions with an appropriate percentage of inert material, such as aluminum oxide, is placed in the boat I 6 and the apparatus is then evacuated, the boat I 6 being heated to a relatively low temperature to drive oi! gas during the evacuation. After an appropriate vacuum is secured, the current through the boat It is increased to cause volatilization of the material therein. The temperature of the boat l6 may be readily ascertained by an optical pyrometer directed thereupon, and once the boat is calibrated the approximate temperature can be determined by an appropriate ammeter in the supply circuit.

The evaporation is preferably performed at a temperature oi. approximately 1000" 0. As the material is evaporated from the boat IE, it condenses on the inner surface of the boat ll, this process continuing until a considerable quantity of the material has been deposited on the inner surface of the latter boat.

After a, suiiicient quantity of the material has been distilled into the boat l1, the temperature is ieduced, air is admitted, and the boat I! removed,

whereupon the material can be removed therefrom; or, if the boat I! is equipped with appropriate terminals, the material may be reevaporated therefrom onto the articles to be coated. In re-evaporating, an approp'irate percentage of a relatively inert material, such as aluminum oxide, should be added to the mixture, as described in the Dimmick application referred to above, in order to control the surface tension of the material and its adhesion.

The prepared material consisting of the evapo rated product and the small percentage of aluminum oxide may be sprayed or otherwise coated onto an appropriate filament such, for example, as one made of tungsten, for evaporation ont optical surfaces; or, as pointed out above, after the material has been removed from the boat and mixed with an appropriate percentatge o1 aluminum oxide, it maybe replaced in the boat for evaporation.

Having now described my invention I claim:

1. A lens coating material consisting of the evaporation product of a mixture of equal molecular parts of calcium fluoride and aluminum fluoride.

2. The method of producing material for reducing the reflection of optical surfaces comprising the steps of mixing calcium fluoride and aluminum fluoride and distilling ofl equal molecular proportions thereof in vacuum.

3. The method of producing material for reducing the reflection of optical surfaces comprising the steps of mixing equal molecular proportions of calcium fluoride and aluminum fluoride,

evaporating in vacuum and collecting the vapor on a relatively cool surface.

4. The method of producing material for reducing the reflection of optical surfaces comprising the steps of mixing calcium fluoride and aluminum fluoride, evaporating off equal molecular proportions thereof in vacuum and collecting the vapor on a relatively cool surface.

5,. The method of producing material for reducing the reflection of optical surfaces, comprising the steps of mixing calcium fluoride and aluminum fluoride, evaporating off equal molecular proportions thereof in a vacuum, collecting the vapor on a relatively cool surface, and mixing the resultant product with aluminum oxide.

JAMES H. REYNOLDS. 

